Engines operating with a variable number of active or deactivated cylinders may be used to increase fuel economy, while optionally maintaining the overall exhaust mixture air-fuel ratio about stoichiometry. In some examples, half of an engine's cylinders may be disabled during selected conditions, where the selected conditions can be defined by parameters such as a speed/load window, as well as various other operating conditions including vehicle speed. A VDE controller may disable selected cylinders through the control of a plurality of cylinder valve deactivators that affect the operation of the cylinder's intake and exhaust valves. Diagnostic methods monitor the valve operation for cylinders switching between VDE and non-VDE modes to ensure proper switching.
One example approach for VDE diagnostics is shown by Bidner et al. in U.S. Pat. No. 5,721,375. In this example, degradation in valve deactivation is identified based on the presence of a pressure difference between an expected and an actual cylinder air charge manifold absolute pressure during VDE modes and the absence of such a pressure difference during non-VDE modes of operation. As such, the actual cylinder air charge value is inferred from a measured engine rotational speed, air mass flow, air and coolant temperature, and a determined barometric pressure.
However, the inventors herein have recognized several issues with such an approach. As one example, in an engine with a large number of cylinders (e.g., six, eight or ten), changes in engine airflow and/or manifold pressure reflective of valve degradation in a single cylinder may not be distinguishable from background noise variation in such parameters. In other words, the individual effect of cylinder deactivation on the overall engine airflow or manifold pressure (at a given engine speed) becomes smaller as the total number of cylinders in the engine increases. Therefore, accurate identification of degradation in a single cylinder valve actuator, for example, may be unavailable. Additionally, since degradation of an intake or exhaust valve may affect flow similarly, the above approach may not accurately distinguish the identity of the valve actuator; that is, whether the degradation affects an intake valve or an exhaust valve.
Thus, in one example, the above issues may be addressed by a method of monitoring cylinder valve deactivation in an engine, the engine including at least a cylinder valve actuator for deactivating at least a cylinder of the engine, the method comprised of an indication of a degradation of the valve actuator, based on crankshaft acceleration.
In one example, the engine is an 8-cylinder engine, such as a V8 engine, that can switch between a non-VDE (V8) mode and a VDE (V4) mode of operation. During a non-degraded steady state V8 mode, the crankshaft acceleration values may be centered around zero. If a significant deviation from this normal acceleration pattern is observed, then valve degradation during V8 mode may be identified. During a steady state V4 mode, the firing cylinders may have positive crankshaft acceleration values while the non-firing cylinders may have negative crankshaft acceleration values of the same magnitude. If a significant deviation from this normal acceleration pattern is observed, then valve degradation during V4 operation may be identified. Further, based on the variation in the crankshaft acceleration pattern from the normal acceleration pattern, the type of the valve degradation (e.g., intake/exhaust) may be identified.
In this way, by monitoring engine crankshaft acceleration values and/or acceleration patterns in an engine for several cycles following a transition into, or out of, a VDE mode of operation, degraded valve operations may be detected at an earlier time, and accordingly addressed in a prompt manner.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.